The present invention relates to molten metal level monitoring and controlling apparatus for continuous casting machines, and more particularly the invention relates to such molten metal level monitoring and controlling apparatus of the type employing an eddy-current type distance measuring device for molten metal level measuring purposes so as to control the level of the molten metal at a predetermined height in the mold.
In the past, measuring means utilizing radiation or thermocouples have been put in practical use for the purpose of molten metal level detection which is necessary for controlling constant the level of the molten metal in the mold of a continuous casting machine.
The measuring means of the type utilizing radition is designed so that as shown by the plane view and the sectional view along the line a--a' of FIG. 1, a radiation source 12 and a scintillator 13 are embedded in the side walls of a mold 10 at the metal level positions so as to detect a molten level 11 on the basis of a change in the amount of the transmitted radiation due to the molten metal, and the detecting means of this type is disadvantageous from safety and sanitation points of view in that the operator must work in the vicinity of the radioactive material.
On the other hand, the measuring means of the type employing thermocouples is so designed that as shown by the plane view and the sectional view along the line b--b' of FIG. 2, a plurality of thermocouples 14 are embedded in the inner surface of the opposing side walls of a mold 10 so as to detect the temperature difference between the position where the mold 10 is not contacting the molten metal and another position where it is in contact with the molten metal and thereby to detect the level of the molten metal, and this type of detecting means is disadvantageous in that the response speed for temperature detection is not high enough and that the response speed is variable depending on the material or thickness of the mold itself.
Moreover, due to the fact that all of these measuring means must incorporate the measuring device inside the mold, they are disadvantageous in that the essential function of the mold itself is deteriorated, that the required maintenance and servicing cannot be effected satisfactorily, and that the measuring accuracy will be limited to about .+-.15 mm. Thus, the problem with the prior art measuring apparatus is that even if the conventional measurement of the molten metal level is effected to maintain the molten metal level constant, the resulting control accuracy and response speed cannot be satisfactory and it is impossible to ensure perfect control of molten metal level, thus deteriorating the surface properties of the cast sections and also tending to cause mold slag inclusion.